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Drilling 304 Stainless

I may have asked this before, but I'm slow:

I have some 304 sheet. I use it to make control-line model airplane handles. Each handle needs to have about 20 1/16" or .050" holes drilled in it, in a pair of tidy lines.

This stuff breaks my regular old HSS drill bits, and my drill hand- sharpening mojo is pretty spotty at 1/16".

I'm using them in a drill press. The whole process feels weird -- it feels like there's a skin on the metal which prevents the drill from starting to cut unless I feed it fairly hard, but once broken through doesn't cause much problem. Most of the time that I break a drill bit it's because I'm feeding it "just a bit harder", then SPING -- I've broken another bit.

Is there a better drill bit to use, or have I just doomed myself to trouble? Is there a better flavor of _stainless_ to use? I understand that 304 is difficult to work with, but it's what McMaster had in the thickness I wanted; having experienced its joys, however, I'm ready to consider something else.

I think my next step is to get a dozen 1/16" drill bits, but if there's some magic material that'll help here, I'm listening.

Reply to
Tim Wescott
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Tim Wescott fired this volley in news:vt2dnVRzqLnrkd3NnZ2dnUVZ snipped-for-privacy@web-ster.com:

Are you center-punching the holes before drilling?

If so, there IS a "skin" to break through... you've work-hardened the piece where it's punched.

A better strategy is to use a really short bit, and just drill.

LLoyd

Reply to
Lloyd E. Sponenburgh

"Tim Wescott" wrote in message news:vt2dnVRzqLnrkd3NnZ2dnUVZ snipped-for-privacy@web-ster.com...

Perhaps you could hone a very fine split point on the drill? That's tiny but could be done with a small diamond file and a steady stroke. It's worth a try.... pdk

Reply to
Phil Kangas

304 SS is junk stainless, but cheap. The reason it's so hard to cut is an absence of sulphur in the alloy for lubrication. You have to get the speed & feed just right to cut it, and you still get short tool life. A few more pennies spent on a better alloy will save a lot in tooling.

Or have the parts cut on a LASER, we cut 304 all day long and the LASERs don't wear out!

David

Reply to
David R. Birch

Tim Wescott fired this volley in news:vt2dnVRzqLnrkd3NnZ2dnUVZ snipped-for-privacy@web-ster.com:

Forgot, Tim...

Even the drilling must be done apace. If you dawdle or idle in the hole, it will work-harden. You must drill smoothly through in one pass, or at least _instantly_ retract the bit if you must stop before penetrating it.

Some coolant or cutting oil will help preserve your edges, too.

LLoyd

Reply to
Lloyd E. Sponenburgh

Any reason not to use 6061T6 aluminum instead??? If you NEED to use stainless, you will NEED a better drill bit. With stainless you need a POSITIVE feed - never let the bit skate on the surface. I'd try a good center punch - or use a "center drill" to make the starting dimple, then follow through with the normal bit. Get one of those that they show at tradeshows etc drilling through files and leaf springs, and using them as milling cutters.

Reply to
clare

I'm thinking very short carbide drills in the CNC mill for precise and consistent feed rate and perhaps some appropriate coolant.

Reply to
Pete C.
304 stainless work hardens if you don't put enough pressure on the drill bit. Also slow is much better than fast, a surface speed of about 50 ft. per minute. If you have a workhardened started hole if you continue drilling the new or sharpened drill will get dull as it cuts the workhardened metal. Once you get through the work hard metal, resharpen or replace the drill or you will wind up with another work hardened hole. You could get a carbide drill that would work much better.

John

Tim Wescott wrote:

Reply to
john

303 stainless will machine and drill much better because of the sulfur content of the metal. The bad part is that 303 doesn't weld well because of the sulfur content.

John

Reply to
john

If you can live with 1/8" thick material, McMaster has 303 SS up to 2" wide. Thin 304 sheet is cold rolled, and consequently work hardened, making it much nastier to machine than hot rolled stock. 303 is a free machining (relatively speaking) grade, and would be the best bet if you can use an available size. But not recommended for welding.

Reply to
Ned Simmons

Aluminum wears too quickly. The holes are for steel line clips, which must bear the centrifugal force of the airplane at the same time that the handle is being worked.

But it would make the job much easier.

Reply to
Tim Wescott

McMaster doesn't carry it, but I suppose that means I should just look around.

Reply to
Tim Wescott

Good thought, but 1/8 is much too thick.

Man, I'm really not trying to reject all advise here...

Reply to
Tim Wescott

Kinda spendy for one-offs. I know a guy who laser cuts balsa -- maybe I'll see what kind of price he'd give me for making a handful of the metal parts, assuming he wants to and can.

Reply to
Tim Wescott

Just a thought... could/would some sort of hardened bushing/fairlead/lead-out work?

It would make the handle assembly lighter as well

Erik

PS, I also flew a lot of C/L as a kid it was the mid/late 60's...

Combat, rat, and even dabbled in a little jet speed.

The hot handle of those days was red plastic, with a piece of cable threaded through it. The ends of the cable had eyes swaged in with 'Nicopress' like sleeves. Not sure of the name... EZ-Just or EZ-Adjust comes to mind...

Reply to
Erik

EZ-Just. I have one.

The hot ticket for control line stunt is a hard-point handle of some sort, with no heavy cable to soften the response by acting as a spring. The handle design I'm using uses a line of holes to adjust spacing, and different-sized clips at the handle to adjust the neutral point. It's exceptionally simple -- except for drilling those damned holes.

Reply to
Tim Wescott

Blink! Blink!

Junk stainless?

I don't think so.

While I'd agree that a change of alloy would be helpful, to imply that this is an inferior alloy is nonsense. It's no such thing. It simply isn't free machining, as you implied, which has no relationship to its quality.

A free machining grade of stainless, if anything, might be considered a somewhat inferior alloy, as the presence of sulfur (or selenium) tends to lower chemical resistance, although improving machining characteristics immeasurably. I

If the article in question can be fashioned from bar stock, that would be my choice---303 S (or Se) stainless. However, that grade is not available as plate, as it does not lend itself to welding, so there is limited need in that configuration.

Harold

Reply to
Harold & Susan Vordos

Tim Wescott fired this volley in news:rcidnaMlKtc7qt3NnZ2dnUVZ snipped-for-privacy@web-ster.com:

So, line the holes with SS grommets/hollow rivets.

It would even "look cool", with the grommets indicating that someone had done something about the wear issue.

Lloyd

Reply to
Lloyd E. Sponenburgh

How thick is the stuff you are drilling?

Stainless work-hardens in a flash - you can't be dainty with it.

Use screw machine bits. Minimize stick-out. You want rigidity - if you could stick a 1/16th collet in the mill and use it as an overbuilt drill press, with the absolute minimum stickout to drill your sheet, that would be lovely. But you should be able to do it in a drill press if it's not terribly sloppy, and you do what you can to minimize stickout, such as buying screw-machine bits.

Heat-Resistant Cobalt Steel Short-Length Drill Bits $1.48 - $1.26 for 12+ (McMaster)

Carbide can be good and bad - it's hard which helps with cutting, but it's brittle so it's prone to break if there is any flex. Plus it costs more than steel.

You might also want to dab a bit of lube on there.

If you have fairly thin sheet, McMaster does seem to have ONE "combined drill and countersink" with a 1/16th drill-point part - that gives you something extra-rigid right down to the top of a very short drill.

2915A72 - kinda spendy at $6.54, but you do get two ends.

Then you have things like...

Straight-Flute Carbide Short-Length Drill Bits for Hard Steel ($11.13) Carbide Small-Diameter Drill Bits with 1/8" Shank ($4.51)

Reply to
Ecnerwal

Carpenter Tech has some excellent literature on machining stainless. I think you have to register to download it, but well worth the effort.

I would also look for cutting lube made for stainless. There are some unusual lubes for stainless including ones with iodine in them. Not sure if any of them are especially good for machining stainless, but Carpenter Tech should have the information.

Dan

Reply to
dcaster

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